If a name is no longer needed, it can be returned to the available pool of domains by navigating to the domain, drilling down and clicking "delete" note that is non-reversible, so be sure that the name is no longer needed. If you decide later to register it again, the registration process would need to be followed, provided that it is still available.
There are 6 domains with a grace period, these are -
co.za.
net.za ,
org.za, jozi.biz,
africa.com,
web.za